There are already known various types of bearing units for supporting a rotating shaft to be rotatable, including a typical one constructed as shown in FIG. 1.
In FIG. 1, the bearing unit is generally indicated with a reference 1020. As shown, the bearing unit 1020 is to support a rotating shaft 1023 to be rotatable. It includes a metallic housing 1022 shaped as a cylinder open at opposite ends thereof and a radial bearing 1021 that supports the rotating shaft 1023 rotatably in the housing 1022. The housing 1022 has installed in one of the open ends thereof a thrust bearing 1024 that supports, thereon in the direction of thrusting, the rotating shaft 1023 supported rotatably in the radial bearing 1021.
The bearing unit 1020 uses a dynamic-pressure fluid bearing as the radial bearing 1021. The dynamic-pressure fluid bearing has formed in the inner circumference thereof opposite to the rotating shaft 1023 in the radial bearing 1021 dynamic pressure producing recesses intended to produce a dynamic pressure.
The housing 1022 is filled with a lubricant that is a viscous fluid and that is circulated through the dynamic pressure producing recesses when the rotating shaft 1023 rotates to produce a dynamic pressure.
The rotating shaft 1023 is inserted in the radial bearing 1021 and received rotatably in the housing 1022, with one end thereof being supported on the thrust bearing 1024.
The housing 1022 has fixed in the other open end thereof a metallic oil seal 1025 formed to have a toroidal shape, and which prevents the lubricant filled in the housing 1022 from leaking out from inside the latter. The rotating shaft 1023 is projected out of the housing 1022 through a shaft insertion hole 1026 formed in the center of the oil seal 1025 and through which the rotating shaft 1023 has been introduced.
To prevent the lubricant filled in the housing 1022 from leaking to outside, an adhesive is used between the oil seal 1025 and housing 1022 to provide a complete sealing at a junction 1027 there. The oil seal 1025 has applied to the inner surface thereof a surfactant to prevent the lubricant from being moved out of the housing 1022 through the shaft insertion hole 1026 under a centrifugal force developed by the rotation of the rotating shaft 1023.
In the bearing unit 1020 constructed as shown in FIG. 1, the lubricant filled in the housing 1022 will flow through only a gap 1031 defined between the outer surface of the rotating shaft 1023 and the inner surface of the shaft insertion hole 1026 (inner surface of the toroidal oil seal 1025). It should be noted that with the gap 1031 reduced in width, the lubricant will have the surface tension thereof increased correspondingly and thus can prevent itself from leaking out of the housing 1022.
Further, the rotating shaft 1023 is tapered (indicated at a reference 1030) at the outer surface thereof opposite to the inner surface of the shaft insertion hole 1026. Namely, the rotating shaft 1023 is tapered outwardly of the housing 1022. The taper surface 1031 will yield a pressure gradient in the gap 1031 defined between the taper surface 1030 itself and the inner surface of the shaft insertion hole 1026, so that a centrifugal force developed when the rotating shaft 1023 rotates will cause a force with which the lubricant filled in the housing 1022 is moved inwardly of the latter. Since the lubricant is thus moved inwardly of the housing 1022 when the rotating shaft 1023 rotates, it will positively enter the dynamic pressure producing recesses in the radial bearing 1021 formed from a dynamic-pressure fluid bearing to produce a dynamic pressure that will assure a stable supporting of the rotating shaft 1023 and prevent the lubricant filled in the housing 1022 from leaking out.
As above, the aforementioned bearing unit 1020 is constructed of the housing 1022, the thrust bearing 1024 and the oil seal 1025, each being an independent member. The number of parts of this bearing unit 1020 cannot be said to be small. In addition, the sealant, such as an adhesive, has to be used to form the oil-tight junction 1027 between the housing 1022 and oil seal 1025, which will cause the assembling of the bearing unit 1020 to be complicated.
Further, use of an adhesive as a sealant will hardly attain any complete sealing at the junction 1027 between the housing 1022 and the oil seal 1025 and permit no positive prevention of the lubricant filled in the housing 1022 from leaking out. To prevent the lubricant from leaking, a surfactant has to be applied to the surface of the oil seal 1025, which also will make the production of a bearing unit of this type more complicated.
As mentioned above, the conventional bearing unit includes many parts and thus is difficult to assemble. No positive sealing of the lubricant is possible. Therefore, conventional bearing units are expensive.
Also, a motor using a bearing unit of the above-mentioned type will be an assembly of many parts, thus difficult to assemble, and so it is not producible with less costs.